1,474 research outputs found
Successful medical management of a domestic longhair cat with subdural intracranial empyema and multifocal pneumonia
On the soliton width in the incommensurate phase of spin-Peierls systems
We study using bosonization techniques the effects of frustration due to
competing interactions and of the interchain elastic couplings on the soliton
width and soliton structure in spin-Peierls systems. We compare the predictions
of this study with numerical results obtained by exact diagonalization of
finite chains. We conclude that frustration produces in general a reduction of
the soliton width while the interchain elastic coupling increases it. We
discuss these results in connection with recent measurements of the soliton
width in the incommensurate phase of CuGeO_3.Comment: 4 pages, latex, 2 figures embedded in the tex
Hole-Pairs in a Spin Liquid: Influence of Electrostatic Hole-Hole Repulsion
The stability of hole bound states in the t-J model including short-range
Coulomb interactions is analyzed using computational techniques on ladders with
up to sites. For a nearest-neighbors (NN) hole-hole repulsion,
the two-holes bound state is surprisingly robust and breaks only when the
repulsion is several times the exchange . At hole doping the
pairs break only for a NN-repulsion as large as . Pair-pair
correlations remain robust in the regime of hole binding. The results support
electronic hole-pairing mechanisms on ladders based on holes moving in
spin-liquid backgrounds. Implications in two dimensions are also presented. The
need for better estimations of the range and strength of the Coulomb
interaction in copper-oxides is remarked.Comment: Revised version with new figures. 4 pages, 5 figure
Effects of interladder couplings in the trellis lattice
Strongly correlated models on coupled ladders in the presence of frustration,
in particular the trellis lattice, are studied by numerical techniques. For the
undoped case, the possibility of incommensurate peaks in the magnetic structure
factor at low temperatures is suggested. In the doped case, our main conclusion
for the trellis lattice is that by increasing the interladder coupling, the
balance between the magnetic energy in the ladders and the kinetic energy in
the zig-zag chains is altered leading eventually to the destruction of the hole
pairs initially formed and localized in the ladders.Comment: final version, to appear in Physical Review
Effect of nonmagnetic impurities on stripes in high-Tc cuprates
We perform the numerically exact diagonalization study of the t-J model with
nonmagnetic impurities to clarify the relation between Zn impurities and the
stripes. By examining the hole-hole correlation function for a two-hole
\sqrt{18}x\sqrt{18} cluster with a single impurity, we find that the impurity
has a tendency to stabilize vertical charge stripes. This tendency is caused by
the gain of the kinetic energy of holes moving along the stripes that are
formed avoiding the impurity.Comment: 3 pages including 2 figures. Proceedings for ISS2000 (Tokyo, October
2000). To be published in Physica
Estudio cuantitativo y estacional de dos poblaciones de cnidarios planctónicos frente a las costas de Barcelona (Mediterráneo Occidental)
Magnetic field effects and magnetic anisotropy in lightly doped La_{2-x}Sr_xCuO_4
The effects of the application of a magnetic field on the diagonal stripe
spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and
0.024). With increasing magnetic field, the magnetic elastic intensity at the
diagonal incommensurate (DIC) positions (1,\pm\epsilon,0) decreases as opposed
to the increase seen in superconducting samples. This diminution in intensity
with increasing magnetic field originates from a spin reorientation transition,
which is driven by the antisymmetric exchange term in the spin Hamiltonian. On
the other hand, the transition temperature, the incommensurability, and the
peak width of the diagonal incommensurate correlations are not changed with
magnetic field. This result suggests that the magnetic correlations are
determined primarily by the charge disproportionation and that the geometry of
the diagonal incommensurate magnetism is also determined by effects, that is,
stripe formation which are not purely magnetic in origin. The
Dzyaloshinskii-Moriya antisymmetric exchange is nevertheless important in
determining the local spin structure in the DIC stripe phase.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Optical conductivity of the Hubbard model at finite temperature
The optical conductivity, , of the two dimensional one-band
Hubbard model is calculated at finite temperature using exact diagonalization
techniques on finite clusters. The in-plane d.c. resistivity, , is
also evaluated. We find that at large U/t and temperature T, is
approximately linear with temperature, in reasonable agreement with experiments
on high-T superconductors. Moreover, we note that displays
charge excitations, a mid-infrared (MIR) band and a Drude peak, also as
observed experimentally. The combination of the Drude peak and the MIR
oscillator strengths leads to a conductivity that decays slower than
at energies smaller than the insulator gap near half-filling.Comment: 12 pages, 3 figures appended, Revtex version 2.0, preprin
Vanishing of the negative-sign problem of quantum Monte Carlo simulations in one-dimensional frustrated spin systems
The negative-sign problem in one-dimensional frustrated quantum spin systems
is solved. We can remove negative signs of the local Boltzmann weights by using
a dimer basis that has the spin-reversal symmetry. Validity of this new basis
is checked in a general frustrated double-spin-chain system, namely the
J_0-J_1-J_2-J_3 model. The negative sign vanishes perfectly for .Comment: 4 pages, REVTeX, 4 figures in eps-file
The susceptibility and excitation spectrum of (VO)PO in ladder and dimer chain models
We present numerical results for the magnetic susceptibility of a Heisenberg
antiferromagnetic spin ladder, as a function of temperature and the spin-spin
interaction strengths and . These are contrasted with new
bulk limit results for the dimer chain. A fit to the experimental
susceptibility of the candidate spin-ladder compound vanadyl pyrophosphate,
(VO)PO, gives the parameters meV and meV. With these values we predict a singlet-triplet energy gap of
meV, and give a numerical estimate of the ladder triplet
dispersion relation . In contrast, a fit to the dimer chain model
leads to meV and meV, which predicts a gap of meV.Comment: 16 pages, 6 figures available upon request, RevTex 3.0, preprint
ORNL-CCIP-94-04 / RAL-94-02
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